In this R01 application we will use a recently developed technique of Non-Invasive Photoconductive Plus Electrical Stimulation (NIPES) of primary rodent hippocampal cultures plated on silicon (Si) chips to ask the question of how exposure to HIV-1 neurotoxins affects the integrity and function of synapses. NIPES of in vitro cultures can be used to model morphologic, neurochemical, and electrical events during synaptic transmission in a non-invasive manner that does not perturb cell membrane integrity and with a cellular resolution that allows investigators that do not have access to two photon microscopy to ask similar sorts of questions using in vitro models. We have recently defined a type of excitotoxic HIV neurotoxin-induced injury to post-synaptic dendritic spines called beading that occurs in vitro, and during normal synaptic activity, is associated with loss of synaptic potentiation. Importantly, beading is also observed in brain tissue from patients with HIV-associated dementia (HAD). Using NIPES to investigate beading is a significant advance in our ability to model pathophysiologic events in in vitro models of HAD because we can selectively and non-invasively stimulate different regions (i.e. cell body vs. axon vs. dendrite) of a neuron. This allows us both spatial specificity and temporal resolution greater than what is currently feasible with other in vitro or slice culture systems to study potential sites of cellular injury to HIV-1 neurotoxins. Using mixed rodent hippocampal cultures grown on photoconductive silicon, we propose two specific aims: (1) Determine whether NIPES of synapses with high frequency stimulation (HFS) will enhance gp120 and/or Tat neurotoxicity at the pre- or post-synaptic level; whether this injury is reversible or irreversible; and whether this injury activates brain derived neurotrophic factor (BDNF) that is involved in synaptic remodeling. (2) Determine microglial responses to dendritic injury (secondary to NIPES of synapses + HFS during gp120 and/or Tat exposure), whether microglial responses affect synaptic transmission, and whether the microglial deactivator minocycline can prevent this type of injury. Because cognitive and motor deficits associated with HAD correlate with simplification of the dendritic arbor and synaptic injury, our ability to understand how neurons communicate with each other and neighboring glia in the Si chip model is important to develop therapies to restore normal synaptic communication. [unreadable] [unreadable] [unreadable]